DE69210993T2 - ELECTROPHORETIC DISPLAY DEVICE WITH SEVERAL ELECTRICALLY INDEPENDENT ANODE ELEMENTS - Google Patents

Description

Technical field of the invention

The present invention relates to an electrophoretic display panel device and a method of manufacturing the same, in particular to a triode-type electrophoretic display panel having an improved anode gate design that allows more efficient electrical connection to the display driver circuit.

State of the art

A variety of electrophoretic display panels are known. Of most direct relevance to the present invention are those described in U.S. Patent No. 4,655,897 entitled "Electrophoretic Display Panels and Associated Methods," U.S. Patent No. 4,742,345 entitled "Electrophoretic Display Panel Apparatus and Methods Therefor," and U.S. Patent No. 4,772,820 entitled "Monolithic Flat Panel Display Apparatus." The foregoing U.S. Patents are issued in the names of Frank J. Disanto and Denis A. Krusos, the inventors of the present application, and are assigned to the assignee of the present application, Copytele, Inc. The display panels shown in the foregoing patents operate on the same basic principle, that is, when a suspension of electrically charged pigment particles in a dielectric fluid is subjected to an applied electrostatic field, the pigment particles will migrate through the fluid in response to the electrostatic field. A substantially homogeneous suspension of particles having a pigment color different from that of the dielectric fluid will, when the applied electrostatic field is localized, cause visually observable localized pigment particle migration. The localized pigment particle migration will result in either a localized area of concentrated or absent particles, depending on the sign and direction of the dielectric force and charge on the pigment particles. The electrophoretic display devices referred to in the aforementioned U.S. patents are triode type displays having a plurality of independent, parallel cathode conductor elements arranged horizontally on a surface of a glass viewing screen. A layer of insulating photoelectric material deposited over the cathode elements and etched into the cathode elements to provide a plurality of insulating strips positioned at right angles to the cathode elements forms the substrate for a plurality of independent, parallel grid conductor elements extending in the vertical direction. A glass cap member forms a fluid-tight seal with the viewing window along the peripheral edge of the cap for containing the fluid suspension and further acts as a substrate for the anode which is a conductor layer applied to the flat inner surface of the cap is applied. With the cap in place, the anode surface is spaced in parallel relationship to both the cathode elements and the gate elements. Given a specific particle suspension, the sign of the electrostatic charge that will attract or repel the pigment particles is known. The voltage of the cathode element and the voltage of the grid element can be assured such that when a certain voltage is applied to the cathode and a different voltage to the grid, the region near their intersection acquires a net charge sufficient to attract or repel the pigment particles in the dielectric fluid suspension. Since multiple cathode and gate lines are used, there are several discrete points that can be controlled by varying the voltage on the cathode and grid elements to locate localized visible areas of pigment concentration and pigment deficiency. It is essential that the operating voltages on the cathode and on the grid must be capable of assuming at least two states corresponding to a logic one and a logic zero. Logical one for the cathode can correspond to either attraction or repulsion of the pigment. Typically, the cathode and grid voltages are chosen so that when a given potential difference of a given polarity exists at a given intersection, there is a sufficient electrostatic field at the intersection to cause the writing of a visual bit of information on the display. In this way, digitized data can be presented on the electrophoretic display.

The electrophoretic display as described above uses various electrically and physically charged cathode and grid elements. For example, an 8-1/2" x 11" display screen with a resolution of 200 lines per inch has 2,200 horizontal cathode elements and 1,700 vertical grid elements. In general, it is desirable to have the greatest number of horizontal and vertical elements with the smallest possible width. This results in increased resolution and screen brightness, that is, the more coordinates, the greater the resolution, the smaller the width of each element, and the less the electrophoretic effect is affected. The electrophoretic display presents a technical requirement that is common in the field of densely packed miniaturized electrical devices, that is, it is possible to use photoetching techniques, etc., to produce extremely small circuit devices, it being sometimes difficult to make the multitude of electrical connections required to integrate the miniature devices, in this case the cathode and grid elements and the display drivers, in a circuit. A variety of methods for facilitating the interconnection of miniaturized devices have been developed. For example, U.S. Patent 4,772,820 teaches an improved means for interconnecting a plurality of miniature cathode and grid elements to display drivers. In accordance with this patent, the ends of the cathode and grid elements lying on the surface of the glass screen of the display device are metallized and grouped into a pattern adapted to electrically connect to corresponding output contacts of a driver circuit bonded to the screen at a predetermined aligned location. Bonding of the respective The connection of the respective contacts is accomplished using wire bonding techniques that can be automated to provide quick and efficient connections. In another aspect of the '820 patent, the inputs to the driver circuit are also wire bonded to patterned input conductors provided on the face of the display to provide a substantially monolithic display screen having integrally associated driver circuits.

Both U.S. Patent No. 4,742,345 and U.S. Patent No. 4,772,820 use a grid consisting of a plurality of electrically and physically independent vertically aligned elements that provide the horizontal coordinate (abscissa) for each displayable location. The grid elements in the aforementioned patents are spaced apart from the cathode elements by an insulating layer. The ends of the connectors and/or electrical connections are made to the screen formed on drive circuits but in the same plane as the cathode elements, i.e., on the surface of the display screen. Each grid element must therefore have a conductive path from the plane of the grid to the plane of the screen surface, which is spaced apart from it by the insulating layer. Since both the grid connector(s) and the cathode connector(s) are arranged on one surface, that is, around the periphery of the field of view, this boundary area is occupied.

It is therefore an object of the present invention to provide an electrophoretic display which avoids the conductor path from the plane of the grid to that of the screen, or, in other words, electrical To create indicator conductors that can rest on the same plane as their conductor ends/connections.

It is a further invention to free up the occupancy of the circuit components and conductor paths around the perimeter of the screen area of an electrophoretic display screen.

It is still a further object to provide an electrophoretic display which can be more easily and economically manufactured by simplifying the connection of the various vertical display elements to their respective drive circuits.

Disclosure of the invention

The problems and disadvantages associated with conventional electrophoretic displays are overcome by the present invention as set out in claim 1 which has a fluid-tight enclosure at least a portion of which is partially transparent to accommodate an electrophoretic fluid having pigment particles suspended therein. The enclosure further comprises a plurality of elongated, substantially parallel horizontal conductor elements arranged in a first plane as well as a plurality of elongated, substantially parallel vertical conductor elements electrically isolated from the horizontal elements and arranged in a second plane. The first and second planes are substantially parallel to each other and the horizontal elements and the vertical elements form a matrix having a plurality of intersection points as viewed along a line perpendicular to the first and second planes. A gate substantially at has the same electrical potential at all its points, is arranged between the horizontal and vertical elements and is electrically insulated therefrom. The grid has a plurality of pores capable of containing the fluid. The horizontal and vertical elements are each selectively electrically chargeable to cause movement of the particles within the fluid, the particles being at least partially visible through the transparent portion of the enclosure.

Brief explanation of the drawings

For a better understanding of the present invention, reference is made to the following description of an exemplary embodiment in conjunction with the accompanying drawings. In the drawings:

Fig. 1 is a schematic plan view of the inner surface of a face plate of a triode-type electrophoretic display panel which, when assembled, forms a fluid-receiving enclosure, would be inside the enclosure and which is in accordance with an exemplary embodiment of the invention.

Fig. 2 is a schematic plan view of the inner surface of a back plate of a triode-type electrophoretic display panel which, when assembled to form a fluid-receiving enclosure, would be inside the enclosure, and which is in accordance with with an exemplary embodiment of the invention.

Fig. 3 is a cross-sectional view of an electrophoretic display panel assembled into a fluid-receiving enclosure using the top plate of Fig. 1 and the back plate of Fig. 2 mounted to an intermediate sealing wall.

Figure 4 is an exemplary row-by-row sequence of voltage state sets for a hypothetical three-cathode element x three-anode element electrophoretic display constructed in accordance with the invention as shown in Figures 1, 2 or 3, where each row listed in the first column has the observable effect on the display resulting from the set of voltage states listed in the subsequent column of that row.

Fig. 5 is a schematic representation of a screen output image resulting from the sequential assumption of the voltage state sets of Fig. 4, assuming the hypothetical 3 x 3 display assumed with respect to Fig. 4.

Best mode for carrying out the invention

Figure 1 shows the back or inside of a cover plate 10 of an electrophoretic display panel 12 (see Figure 3) in accordance with the present invention. The anode conductors shown on the back plate in Figure 2 are shown in phantom in Figure 1. The cover plate 10 is typically formed of glass and serves as a substrate onto which a plurality of independent, electrically conductive cathode elements 14 (horizontal rows) are deposited using conventional deposition and etching techniques. It is preferred that the cathode elements 14 be made of indium titanium oxide (ITO) as described in U.S. Patent No. 4,742,345 (which patent is incorporated herein by reference) which teaches an exemplary method of forming the cathode elements 14. A grid 16 overlies the cathode elements 14 and is insulated therefrom by a spaced photoresist layer 18 (see Fig. 3). The grid 16 is an electrically equipotential element, that is, the entire grid is in electrical continuity. The grid 16 may be formed by coating the photosensitive layer 18 with a metal such as nickel using a spatter technique or the like, and then masking and etching a plurality of pores 20 through the metal layer, or by depositing a plurality of grid lines in one direction and then laying another set of grid lines perpendicular thereto in an electrically conductive relationship. Regardless of which method is used, the resulting grid 16 preferably has a pore size of approximately 10 µm, a pore-to-pore center-to-center spacing of about 20 µm, and a Grid thickness of approximately 3,000Å. Gate 16 is provided with a single conductor post 22 leading therefrom to a terminal 24 for receiving a voltage source. Consequently, the entire grid 16 is maintained at a single electrical potential over the entire area during operation of the display. This is in contrast to previous grid structures which were formed from discrete elements which can assume a variety of voltages during operation corresponding to the display operations of erase, hold and write. The present invention uses electrically and physically discrete anode elements 26 (see Fig. 2) to provide the horizontal coordinate (abscissa) indicating where the display operations occur, instead of discrete grid elements previously used. The mounted position of the anode elements 26a with respect to grid 16 and cathode elements 14 is indicated in dashed lines in Fig. 1. As with the earlier displays, see for example U.S. Patent No. 4,742,345, each cathode element 14 terminates at one end in a contact pad 28 which is merely an enlargement of the element which makes the connection to the display driver circuit 30. Of course, if the connections 32 are printed in the same process as the cathode elements 14, for example, the contact pads 28 are not required. The same components form the anode elements 26, which are described below. In the embodiment shown, an exemplary row driver circuit 30 is bonded to the cover plate in accordance with the teachings of U.S. Patent No. 4,772,820, which is incorporated herein by reference. An actual display would include a plurality of such circuits as described in U.S. Patent No. 4,772,820. The number of cathode elements 14 shown is three, which is considerably reduced for ease of illustration. Actual displays would have on the order of 2,200 such cathode elements 14. An input terminal 34 is shown connected to each driver circuit 30 for purposes of illustration. More accurate representations of the number and arrangement of such input terminals 34 are shown in U.S. Patent No. 4,772,820.

Figure 2 shows the front or inside of a back plate 36 of an electrophoretic display panel 12 (see Figure 3) in accordance with the present invention. The back plate 36 is preferably made of glass and serves as a support on which a plurality of independent, electrically conductive anode elements 62 (vertical rows) are mounted. It is preferred that the anode elements 26 be formed of a metal, such as chromium. In addition to the fact that they connect the anode elements 26 to the cathode elements 14, the anode display driver circuits 38, the connections 40 from the anode element contact pads 42 to the circuits 38, and the anode input terminals 44 have the same shape and function as the corresponding elements connected to the cathode elements 14 and described with reference to Figure 1. It should be noted that the anode elements 26, their contact pads 42 and all connections to anode driver circuits 40, as well as the anode driver circuits 38 and the anode input terminals 44 each rest on the surface of the back plate 36. This design does not require a multitude of electrical connections to be made between the elements arranged in different planes. By using the anode elements 26 instead of separate grid elements to create the abscissa of a display coordinate pair, the undesirable connections between two planes are avoided. Since the vertical anode elements 26 and their connections and driver circuitry are arranged on the back plate 36 instead of the face plate 10, the occupancy around the periphery of the face plate is reduced to about half.

Figure 3 shows that the face plate 10 and back plate 36 of Figures 1 and 2 are sealingly secured to a peripheral sealing wall 46 to form an enclosure for containing a dielectric fluid/pigment particle solution (not shown). The face plate 10, back plate 36 and wall 46 are sealingly joined by an adhesive, heat welding or any other conventional method for forming sealed glass enclosures. It should be noted that the pores 20 of the grid 16 extend through the grid 16 and also through the insulating photoresist layer 18 so that the electrophoretic fluid is in contact with the cathode elements 14 via the pores 20. The extension of the pores 20 through the photoresist layer 18 can be formed by the conventional methods and techniques such as those described in U.S. Patent 4,742,345. The dimensions of the cathode elements 14, the insulating layer 18 of the grid 16 and the anode elements 20 are all greatly exaggerated for ease of illustration. In fact, the cathode elements are preferably about 1,200 Å thick, the grids about 500 Å thick and the anode elements 26 about 3,000 Å thick. By applying voltages to the cathode elements 14, the grid 16 and the anode elements 26, the suspended pigment particles in the dielectric fluid can be arranged close to the intersections of the selected cathode and anode elements, or remote therefrom, to apply these voltages to a visible display. These characteristics, except for the respective functions of the grid 16 and the anode elements 26, are in accordance with U.S. Patent 4,742,345, to which reference is made for further details of the arrangement and function of the display 12.

Reference is now made to Figure 4 which is a table of voltages applied to the hypothetical 3 x 3 display. Each row shows the effect on the display of various combinations and voltages applied to the 3 cathode elements (R1, R2, R3) and the 3 anode elements (C1, C2, C3). Note that the grid voltage is held constant in all voltage sets. The voltages V1, V2 and V3 are a function of the amount of spacing from the anode elements 26 to the grid 16 and cathode elements 14. The spacing is chosen to minimize the leakage of the electrostatic field between such elements at the display points, since such leakage results in reduced resolution. Assuming a gap of 3 mm between the front plate 10 and a back plate 36, the voltage levels would be approximately as follows: V1 = 50 V, V2 = 18 V and V3 = 10 V. The grid 16 would remain at approximately -4 V.

Figure 5 shows the visual effect on a hypothetical 3 X 3 display achieved by applying the sequence of voltage sets shown in the table of Figure 4 to a hypothetical 3 X 3 display constructed in accordance with the present invention, wherein the dark blocks represent a Display bit in the described or "ON" state.

It is to be understood that the embodiments described here are merely exemplary and that those skilled in the art can make various variations and modifications without departing from the scope of the invention as set forth in the appended claims.

Claims (19)

1. An electrophoretic display device (12) comprising: (a) a fluid-tight enclosure, one portion (10) of which is at least partially transparent; (b) an electrophoretic fluid received in the enclosure, the electrophoretic fluid having pigmented particles dispersed therein; (c) the enclosure further comprising a plurality of elongated, substantially parallel horizontal conductor elements (14) arranged in a first plane (14); (d) a plurality of elongated, substantially parallel, vertically extending conductor elements (26) electrically insulated from the horizontal conductor elements (14) and distributed in a second plane, the first and second planes being substantially parallel to each other, the horizontal and vertical conductor elements (14, 26) forming a matrix having a plurality of intermediate sections, viewed along a line perpendicular to the first and second planes; and (e) a continuous electrically conductive grid (16) such that all points thereof have the same potential, the grid (16) being fixedly disposed between and electrically insulated from the horizontal and vertical conductor elements (14, 16), the grid (16) having a plurality of pores (20) capable of receiving the electrophoretic fluid therein, the grid (16), the horizontal conductor elements (14) and the vertical conductor elements (16) being selectively electrically charged to cause movement in the particles within the electrophoretic fluid, the particles being at least partially visible through the at least partially transparent portion (10) of the enclosure. 2. The device according to claim 1, wherein the enclosure has a substantially flat viewing plate (10) whose central portion is the at least partially transparent portion of the enclosure, the viewing plate (10) forming a substrate that supports the horizontal conductor elements (14) in the first plane. 3. The device of claim 2, wherein the enclosure has a back plate (36) forming a support that supports the vertical conductor elements (26) in the second plane. 4. The device of claim 3, further comprising a layer of insulating material (18) overlapping the horizontal conductor elements (14), the grid (16) being applied to the layer of insulating material (18) remote from the horizontal conductor elements (14). 5. The device of claim 4, wherein the layer of insulating material (18) is penetrated by a plurality of holes that allow the electrophoretic fluid to contact the horizontal conductor elements (14). 6. The device of claim 5, wherein the bores at least partially communicate with the pores (22) such that the fluid can flow through the pores (20) and in the bores. 7. The device of claim 6, wherein the electrophoretic display is of the triode type, in which the horizontal conductor elements (14) form a cathode, the grid (16) is a gate of the triode, and the vertical conductor elements (26) form an anode of the triode. 8. The device of claim 7 further comprising a side wall (46) disposed between and sealingly connected to the face plate (10) and the back plate (36) to create the fluid-tight enclosure. 9. The device of claim 8, wherein the visible panels (10) are made of glass and the horizontal conductor elements (14) are formed of indium tin oxide. 10. The device of claim 9, wherein the back plate (36) is glass and the vertical conductor elements (26) are at least partially formed of chromium. 11. The apparatus of claim 6, wherein each of the plurality of elongated, substantially parallel horizontal members (14) and each of the plurality of elongated, substantially parallel vertical conductor members (26) have one end for electrical connection to an associated voltage source and one free end. 12. The device of claim 11, wherein the electrical connection ends and the free ends of successive ones of the horizontal conductor elements (14) are positioned in proximity to each other on the surface of the face plate (10). 13. The device of claim 12, wherein the electrically connecting ends and the free ends of adjacent ones of the vertical conductor elements (26) are positioned in proximity to each other on the surface of the back plate (36). 14. The apparatus of claim 11, further comprising at least one row display driver circuit (30) mounted on the face plate (10) and electrically connected to the horizontal conductor elements (14) by electrical connectors (32). 15. The apparatus of claim 14, further comprising at least one column display driver circuit (38) attached to the back plate (36) and electrically connected to the vertical conductor elements (26) via electrical connectors (40). 16. The apparatus of claim 15, wherein the horizontal conductor elements (14), the at least one row display driver circuit (30), and the electrical connectors (32) therebetween all rest substantially in the first plane. 17. The apparatus of claim 16, wherein the vertical conductor elements (26), the at least one column display driver circuit (38), and the electrical connectors (40) therebetween all rest substantially in the second plane. 18. The apparatus of claim 17, further comprising input terminals (34) disposed on the light panel (10) in the first plane for the at least one row display driver circuit (30). 19. The apparatus of claim 18, further comprising input terminals (44) disposed on the backplate (36) in the second plane for the at least one column display driver circuit (38).